1. Field of the Invention
The invention relates to a middle ear prosthesis with a tubular housing. The prosthesis replaces eardrum (tympanic membrane) and ossicles of the middle ear which have been destroyed by otitis or similar.
2. Description of the Prior Art
It is presently known to repair the sound receiving and conducting mechanismus of the middle ear by surgical implantation of various types of prosthesis. Such repair involves total reconstruction of all three ossicles and the ear drum.
Such a middle ear prosthesis is known out of DE 4 407 847 A1. The tubular housing of this prosthesis is not only closed at its outwards showing end by an outer membrane replacing the eardrum. It is also provided at its inner end with an inner membrane. Said inner membrane is joined to the outer membrane by a transmission link that is located inside and that prestresses inwards outer and inner membrane. The surface of the outer membrane is bigger than the surface of the inner membrane. Sound transmission from the inner membrane to the stapes base plate occurs by a small quantity of the patient's own fat. This fat required for sound transmission is located outside the prosthesis between the inner membrane and the stapes base plate.
A disadvantage of this known middle ear prosthesis is that the achievable sound pressure at the stapes base plate is not high enough for normal hearing, since the transformation ratio of the two membranes is reduced. Furtheron the transmission path of the sound between the inner membrane and stapes base plate is subject to unsteadiness since the smallest inclusion of air in the fat or its dwindling and the thus occurring smallest air gap are already strongly influencing the transmission of sound.
EP 460 354 B1 discloses a middle ear prosthesis that does without its own housing. The artificial eardrum is tentered in an outer retaining ring inserted in a recess made especially for said ring in the petrous bone. The eardrum has a hole in its centre into which a thickened front area of an ossicle-substitute may be fitted. Thus, the ossicle-substitute may in a first place be arranged in the space behind the artificial eardrum. Then, the artificial eardrum is inserted, whereas the front end of the ossicle-substitute snaps into the hole of the eardrum.
Further middle ear prostheses are known out of EP 281 047 B1, DE 2 905 183 C3, DE 2 937 842 C3 and EP 203 785 B1.